Coverage analysis tool for optical data#
This module uses the sepal_ui framework and interactive Voila dashboard to create maps of cloud-free observations for major optical satellites available on the Google Earth Engine (GEE) platform.
The three-step process is described in the following sections.
Select an area of interest (AOI)#
Using the provided AOI selector, select an AOI from the available methods. We provide three administrative descriptors (from level 0 to 2) and three custom shapes (drawn directly on the map, asset or shapefile).
If a custom AOI from a shape or drawing is selected, you will be able to use it directly. The upload to GEE will be launched in the background.
Select dataset parameters#
To perform BFAST pre-analysis, provide the tool with key parameters:
Date range: the start and end date of your analysis
Sensors: the list of sensors you want to use (Landsat missions and Sentinel-2)
Tier 2: Tier 2 images of the Landsat missions (note: this might lead to incorrect results)
SR: whether to use surface reflectance (SR) images (by default, top of atmosphere [TOA])
Once all parameters have been chosen, select the button.
After selecting your parameters, move to the Visualization tile.
Select one of the statistical measures to display in the following list:
cloud-free pixel count
total pixel count (i.e. scene coverage)
NDVI Std. Dev.
You can also produce stats on a yearly basis using the provided switch.
The image will be dynamically re-evaluated and recentred upon each change.
When you’re satisifed with the displayed information, it can be exported for further use in GIS software or a GEE process. The tool provides two main exportation options: as an asset (in GEE) or a .tif file (in SEPAL).
Both use the GEE export system and share the same set of parameters:
statistical measures to export
count of cloud-free observation per pixel
NDVI’s median of cloud-free observations
NDVI’s std. dev. of cloud-free observations
count for all observations per pixel
full timespan calculation(s)
scale: the resolution (in metres) to use in the exported GEE file
When exporting the image to SEPAL, you cannot quit the application until the download is finished.